ENDURING CONSEQUENCES OF NEONATAL TREATMENT WITH ANTISENSE OLIGODEOXYNUCLEOTIDES TO ESTROGEN-RECEPTOR MESSENGER-RIBONUCLEIC-ACID ON SEXUAL-DIFFERENTIATION OF RAT-BRAIN

Sexual differentiation of the mammalian brain is regulated by steroids during a critical developmental period, particularly by estradiol, wh ich is believed to be aromatized in brain from gonadally derived testo sterone. To ascertain the importance of neuronal estrogen receptor exp ression during sexual differentiation, we infused a 15-mer oligodeoxyn ucleotide antisense to the region of the translation start codon of es trogen receptor messenger RNA (mRNA), into the hypothalamus of 3-day-o ld rat pups. Two separate control treatments consisted of either a scr ambled nucleotide sequence oligodeoxynucleotide, which had little homo logy to known mRNAs, or vehicle. Female pups either received a lightly androgenizing dose of testosterone 6 h after oligo infusion or were n ot hormone treated. Infusion of antisense oligo to estrogen receptor m RNA protected against many of the androgenizing effects of testosteron e. Androgenized females infused with antisense oligo were significantl y more likely to exhibit female sexual behavior in adulthood after tre atment with estrogen plus progesterone and remained sensitive to the i nduction of wheel-running behavior by estrogen treatment seen in norma l females, whereas the control androgenized females did not. Normal fe males did not exhibit any effects of antisense oligo treatment on sexu al or locomotor behavior, but antisense oligo-treated normal females s howed a trend (P = 0.09) toward disrupted estrous cyclicity and behave d differently in tests of open field behavior compared to controls. Af ter killing, brains were processed for histology. Morphometric analysi s of the sexually dimorphic nucleus of the preoptic area demonstrated a significantly smaller volume in antisense oligo-infused androgenized females compared with vehicle and scrambled oligo-infused controls. T he sexually dimorphic nucleus volume was smaller still in normal femal es infused with antisense oligo, consistent with estrogen receptor act ivation playing an active role in sexual differentiation of the female brain. These results demonstrate the effectiveness of antisense oligo deoxynucleotides in permanently altering a developmental process if ad ministered during a critical period.